A drag race is a race between two racing vehicles (typically cars or motorcycles) from a standing start to a finish line that is up to a quarter mile away down a straight race track. A drag race is started by a vertical series of lights, called a “Christmas tree,” that sequentially light yellow lights followed by a green light that starts the race. The objective of a drag race is to reach the finish line in less time, after the green light starts the race, than does the opponent. The time to reach the finish line is the total of two parts of the race: the length of time between the green light signaling that the race has started and the vehicle leaving the starting line (commonly referred to as the Reaction Time), and the time between leaving the starting line to reaching the finish line (commonly referred to as the Elapsed Time or ET). Electronic timers measure both the Reaction Time and ET.
Some types of drag racing limit the cars to a selected ET. In those races, examples of which are referred to as “Bracket Racing” or “Super Class Racing”, the driver, the race track, or the race sanctioning association selects the ET that the car should run. This is known in racing as the Dial In. The object of a drag race in which the cars each have a Dial In is for the car to reach the finish line ahead of the opponent and do so with an ET that is equal to or larger than the Dial In. If the racer goes quicker than his Dial In and his opponent does not, then his opponent wins the race. If both racers go quicker than their Dial Ins, the racer who goes furthest under his Dial In is disqualified and his opponent wins.
In Super Class racing, both cars are assigned the same Dial In and therefore, both cars leave the starting line at the same time. They race each other and try to finish first without going quicker than the assigned Dial In.
In other ET or Bracket racing, a slow car can race a fast car by having the race track handicap the fast car by permitting the slower car to start the race first. This is done using a Christmas Tree that has a series of lights for each car. The Christmas Tree lights for the slower car are lighted a selected amount of time before the lights for the faster car. Handicapping allows the slower car to start first by an amount of time that is equal to the difference between the Dial Ins of the two cars (the handicap). In theory, if both cars leave the starting line exactly when their respective green Christmas tree lights turn on, and they run perfectly on their Dial In, they should cross the finish line at the same time.
The purpose of this type of racing is to minimize the cost of campaigning a race car. A car that competes in Super Class or ET racing need not be at its performance limit to compete. Cars are built to reliably perform well enough to complete the race at the Dial In. In the Super Classes, where the Dial In is assigned by the track or the race sanctioning body, and in other ET racing, the race car engines produce enough power so that the car can run quicker than the Dial In under track or weather conditions that cause a car to run slower than normal. A car having more power than required to run its Dial In can always run too quickly under normal conditions and so it must be slowed down to avoid disqualification for running under its Dial In.
Devices known as “throttle stops” were created to selectively limit the power of race car engines to prevent the car from completing the race with an ET that is less than its Dial In. A throttle stop adjustably controls the engine throttle to set the engine power level up or down to allow the car to run at exactly the Dial In regardless of the track or weather conditions. An additional benefit of using a throttle stop is that it can be turned on and off (changed from limited or throttle stopped power to full power) as the car goes down the track. This usually results in a car having a higher speed at the end of the track than would normally be expected for a car that runs the selected Dial In. This is a particular advantage for a faster car that is chasing a slower car because the faster car driver can judge both how fast he is closing in on the slower car and when he will cross the finish line, and can decide whether to release a throttle stop to increase the car's speed. The slower car driver must continually look over his shoulder to see the faster car coming up behind him and then he must turn around to look at the finish line. These advantages of “throttle stops” have made them widely used and well known.
There are various types of throttle stops, including a “linkage style” throttle stop and a “baseplate style” throttle stop.
A linkage style throttle stop (see, for example, Dedenbear Products, Inc. catalog, volume 9, page 19 model TS-10) includes a collapsible link that is part of the throttle linkage between the gas pedal and the engine's fuel metering device (carburetor or fuel injector). The length of the collapsible link changes thereby changing the position of the butterflies on the fuel metering device to either a more closed position to limit the amount of air flow and engine power or to a more open position to increase engine power. This style throttle stop is inexpensive and easily adaptable to many types of fuel metering devices. A disadvantage of the linkage style throttle stop is that most racing fuel metering devices do not perform well under partial throttle conditions and therefore the car's performance becomes erratic.
Another type of throttle stop is the baseplate style. In this throttle stop, a baseplate is mounted under the fuel metering device. The baseplate has openings through which air and fuel from the fuel metering device enter the engine. Conventional baseplate throttle stops have a set of butterflies mounted in the baseplate openings. The baseplate butterflies open and close to control the total air/fuel mixture flow into the engine after the fuel has been injected into the airstream by the fuel metering device. The advantage of this type of throttle stop is that at all times during a race, the fuel metering device runs at its optimum condition of its wide open position so that the fuel metering and therefore the car performance stays very consistent. This style of throttle stop was created in 1987 by Dedenbear Products, Inc. and has been used to win many World drag racing championships (see Dedenbear Products, Inc. catalog, volume 9, pages 16-17 models TS-1 and TS-5).
An improvement of baseplate style throttle stops that is best described as a “disc” style stop is disclosed by U.S. Pat. No. 6,189,505, which is incorporated herein by reference. This throttle stop has, in one embodiment, two counter rotating discs that are stacked on top of each other. Each disc has holes that match the bores of a fuel metering device. As the discs are rotated toward the closed condition, the holes start to overlap and block each other, which chokes off the air/fuel flow. Rotating the discs to the fully open position results in substantially perfect open bores (holes) that match the fuel metering device bores. In this position, there is substantially no restriction to air/fuel flow so maximum engine horsepower is achieved.
All types of throttle stops require an actuator to activate the throttle stop mechanism. Actuators have typically been an electric solenoid or a pneumatic cylinder that move the throttle stop mechanisms.
Electric solenoids are desirable because they are very simple, reliable, and inexpensive. The drawback to using an electric solenoid is that it opens and shuts instantaneously. On a car with a high horsepower engine, opening and shutting the throttle stop quickly can often cause the car's rear drive tires to spin (lose traction) due to the abrupt change in the engine power level and driving becomes dangerous.
Because of this problem, pneumatic actuators are often used. Adjustable flow limiters in the air supply lines to a pneumatic actuator regulate the speed that the pneumatic actuator moves and therefore how fast the throttle stop opens and closes. By setting the speed that the stop opens and closes, a smooth transition from full power to limited power and vice versa results and the car remains stable as it goes down the track.
A disadvantage of both pneumatic and solenoid actuators is that they tend to open and close at the same speed for their entire stroke. For solenoids that speed is undesirably fast. For pneumatic actuators that speed is not always the same for different strokes, as the rate of actuation can change due to supply pressure or temperature variation.